Recently, noble metal growth and in particular ruthenium growth by atomic layer deposition (ALD) has attracted interest as an enabling material in future technology nodes for several applications, such as dynamic random access memory (DRAM) and interconnect metallization.
For DRAM metal-insulator-metal capacitors (MIMCAP), Ru and/or RuO2 but also other noble metal(s) (oxides) are candidates to replace TiN electrodes in metal-insulator-metal capacitor structures. Ru has the advantage, when compared to other metals, of being still conducting when oxidized and hence does not contribute to the equivalent oxide thickness (EOT) of the capacitor. Moreover, RuOx has the advantage of reducing the leakage by trap density reduction of dielectrics such as strontium titanate (STO).
Electrochemical deposition of Cu for interconnect metallization traditionally uses Physical vapor deposition (PVD) of a Cu seed layer on top of a PVD Ta/TaN barrier to conduct the current. However, the step coverage limitations of the PVD technique compromise its use in future technology nodes. Barriers grown by deposition Atomic Layer Deposition (ALD) combined with seedless Cu electroplating is one of the metallization routes explored for sub-25 nm line critical dimensions (CD's). However, compatibility with seedless electroplating seriously limits the choice of materials. Among the different candidates, Ru layers have been identified as very promising to act as nucleation layers for direct Cu plating. Furthermore, high electromigration resistance has been demonstrated in for Cu metallization using a CVD Ru-liner showing that Ru is a valuable replacement for the conventional Ta. Next to the compatibility with Cu, Ru has a low resistivity which is very important for interconnect applications.
Ru, and in particular RuO2 as well as other noble metal(s) (oxides) could also be of interest because of its high effective workfunction (EWF) for metal gates in complementary metal oxide semiconductor (CMOS) transistors or other applications like resistive random access memory (RRAM) as high EWF electrode.
It is known that ALD noble metal growth is highly substrate dependent. On Si oxides for example, large incubation times have been observed, while on metal nitrides, the incubation time is substantially less. US 2010/0136776 discloses that when differences in incubation periods are large enough, selective growth is possible on selected areas of the substrate; for example when depositing Ru on a substrate comprising oxide surfaces and metal nitride dots, Ru will grow selectively on the metal nitride dots.
Selective growth of noble metals is of interest in various areas, such as selectively growing the metal gate in transistors, bottom up fill in interconnects. Furthermore, the trend towards 3D devices will require depositions in complex structures with complex shapes.
However, when oxides cannot be used to enable selective growth on metal substrates, for example due to the incompatibility with the process flow, such as harmful oxidation of (parts of) the substrate during the oxidation deposition process, using the incubation time difference between oxide and metal (nitride) substrate is not possible.
Furthermore, when selective growth is only required up to a certain thickness and needs to be followed by a non-selective growth, more than one deposition chamber and/or technique needs to be used and this is unwanted.